just-the-docs/docs/tests/navigation/order/strings/index.md

layout	title	parent	nav_order	has_children
default	Strings	Order	2	true

String Order

By default, all Capital letters come before all lowercase letters; you can add nav_sort: case_insensitive in the configuration file to ignore the case).

Digits precede letters, and numeric titles are ordered lexicographically: "10" precedes "2" (in contrast to explicit numeric nav_order values).